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Steph's choice at this time was between purchasing an electric car or installing an air source heat pump at her home. When factors such as home heating accounts for 38% of all UK gas use, an average household gas boiler emits greenhouse gases equivalent to approximately 2.2 tonnes of CO2 per year (Source: NESTA), and the £7,500 grant from the government for a heat pump installation were taken into account the decision to opt for an air source heat pump was a bit of "no-brainer".

 

About the home

Steph has lived in a semi-detached house in Cookham, near Maidenhead since 1997. It was constructed in the mid 1960s of brick and tiles and in 2009 a well-insulated single storey extension was added, with underfloor heating, an induction hob and a new gas combi-boiler. In 2015 ten solar panels were installed on the south-facing roof under the government’s FIT scheme and in 2021 the insulation in the loft was topped up and the loft hatch insulated. In 2022 Cavity wall insulation (an expanded polystyrene bead coated with an approved adhesive) was injected to reduce thermal heat loss. 

 

After installing cavity wall insulation Steph's gas usage fell 28% in the first year while, according to her records, her annual gas usage fell by 42% between 2019 and 2023 as a result of these measures, while her electricity usage remained the same.

 

Motivations for installing an air source heat pump

Having improved the insulation in her home, the next obvious step to going zero carbon was to replace the 15-year-old gas combi boiler. A ground source heat pump had been considered when the extension was built but was too costly. Steph investigated an air source heat pump solution in 2023-24 by attending talks at the Eco Action Hub in Maidenhead and from Toby Knight of Cookhams Footprint, where she learned that in October 2023 the grant level for air source heat pumps had increased to £7,500 per household. Toby invited her to his home to see his heat pump in action and she decided to take the zero-carbon route.

 

Appointing a contractor

A representative of a recommended local firm, Hepplethwaite Red Van plumbers, visited her property, took measurements to evaluate the size of heat pump required and answered all her questions, without pressuring her for a decision. They came back with an acceptable quote and start date. A longstanding Grant installer, they specified the Aerona 3 (a UK product) because of the build quality and level of service the manufacturer provided. Steph decided against replacing the radiators upstairs as she likes to sleep in a cool room, so will continue to adjust heating levels in each room using thermostat control valves; she'll control the temperature in the bathroom via the thermostat upstairs.

 

What measures were installed?

On the roof of the single storey extension a 14-kwH air source heat pump was installed. In the loft, the boiler was removed and a hot water tank installed. The work took eight days.